Use of carbon dioxide and carbonic acid to clean contact lenses

ABSTRACT

Simple, efficacious, easily manufacturable, convenient to use and cost-effective contact lens care cleaning compositions comprising carbon dioxide and carbonic acid as cleansing agents are disclosed. The compositions do not require abrasive agents such as polymeric beads, nor ocularly irritating agents such as enzymes or surfactants in order to effectively clean proteinaceous and nonproteinaceous deposits from the surface of contact lenses. Also disclosed is a one-step cleaning and disinfecting regimen, whereby an effervescent tablet composition capable of generating carbon dioxide and carbonic acid is dissolved in a disinfecting solution or rinsing/disinfecting/storage solution.

This application is a continuation-in-part of Ser. No. 09/099,669 filedJun. 18, 1998, now U.S. Pat. No. 5,909,745 which is acontinuation-in-part of Ser. No. 08/806,571, filed Feb. 25, 1997abandoned, which claims priority from provisional application, Ser. No.60/012,274, filed Feb. 26, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to contact lens cleaning methods andcompositions. In particular, this invention relates to the use of carbondioxide and carbonic acid to clean contact lenses.

2. Description of Related Art

Numerous contact lens care cleaning compositions are known. Contact lenscleaning products typically contain polymeric beads, enzymes,surfactants, or some combination thereof, as cleansing ingredients.Repeated use of cleaning compositions containing polymeric beads, suchas Teflon or silicon dioxide beads, can damage the surface of contactlenses. Additionally, if all polymeric beads are not rinsed from thelens before inserting the lens in the eye, any residual beads mayirritate the eye.

Enzymatic cleaners are popular cleansing agents for contact lenses,particularly for their ability to remove protein deposits. Raw materialcontrol for both enzymes and polymeric beads is often difficult. As inthe case of polymeric beads, enzymes can be irritating to the eye if notthoroughly rinsed from the contact lens before it is inserted.Enzyme-containing cleaning products also suffer the disadvantage thatthey are generally incapable of being sterilized with heat, as the hightemperatures required for sterilization can chemically degrade enzymes.

Surfactants are typically ineffective for cleaning protein deposits andare also generally irritating to the eye.

JP 01179123A (890717) discloses contact lens cleaning compositionscontaining percarbonate and an anionic or nonionic surfactant. Thereaction of percarbonate with water generates oxygen bubbles. Thereference attributes the cleaning to the mechanical cleaning action ofthe bubbles and the chemical cleaning action of the surfactant.

EP 93784A (831116) discloses enzymatic cleaning compositions for contactlenses. The cleaning compositions are comprised of an effervescenttablet containing trypsin, alpha-amylase, lipase, citric acid, sodiumbicarbonate, calcium acetate and EDTA.

JP 88059123B (881117) discloses a foaming, contact lens cleaning tabletcomposition containing sodium bicarbonate, an organic or inorganic acid(or salt thereof), an enzyme, and a surfactant. When combined with cleanwater, the reference tablet foams, removing stains from the surface ofcontact lenses by the physical action of the foam. After foaming,remaining stains are removed by the enzyme and the surfactant.

Therefore, it is highly desirable to have lens care cleaningcompositions which are capable of effectively cleaning proteinaceous andnonproteinaceous deposits from lenses, but which do not require thepresence of polymeric beads, enzymes or cleansing amounts ofsurfactants.

SUMMARY OF THE INVENTION

The present invention provides contact lens care cleaning compositionscomprising a cleansing amount of carbon dioxide and carbonic acid, orwhich are capable of generating a cleansing amount of carbon dioxide andcarbonic acid. Because the compositions of the present invention do notrequire polymeric beads, enzymes or cleansing amounts of surfactants,they are much less likely to damage the surface of a contact lens orcause ocular irritation.

The present invention also provides a simple method of cleaning contactlenses. The method comprises contacting the lens in need of cleaningwith carbon dioxide and carbonic acid for a time sufficient to achieveeffective cleaning.

In the most preferred embodiment, the present invention provides aone-step cleaning and disinfecting system for contact lenses. A cleaningand disinfecting solution is prepared by dissolving an effervescenttablet in an ophthalmically acceptable disinfecting solution at a pH ofless than about 7.5 such that carbon dioxide and carbonic acid aregenerated, and then the soiled contact lens is contacted with theresulting solution for a time sufficient to achieve effective cleaningand disinfection in a single step.

Among other factors, the present invention is based on the finding thatsoiled contact lenses can be effectively cleaned by compositionscomprising a cleansing amount of carbon dioxide and carbonic acid,without the need for additional cleaning agents, such as polymericbeads, surfactants or enzymes, typically present in the contact lenscare cleaning compositions currently marketed.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a comparison of the cleaning efficacy of cleaning solutions(with and without carbon dioxide).

DETAILED DESCRIPTION OF THE INVENTION

The contact lens cleaning compositions of the present invention comprisea cleansing amount of carbon dioxide and carbonic acid. Suchcompositions may contain carbon dioxide and carbonic acid in theirfinal, packaged formulation, as in the case of compositions containingcompressed carbon dioxide and water in a pressurized container. Forexample, carbon dioxide could be used as the pressurizing gas in anaerosol can containing purified water, a simple contact lens storagesolution, or an aqueous-based multi-purpose contact lens composition,including the commercially available rinsing, disinfecting and storagesolutions known as Opti-Free or Opti-One Express.

Alternatively, the compositions of the present invention may beformulated to generate carbon dioxide and carbonic acid to clean contactlenses. For example, effervescent tablets may be prepared which, upondissolution in water or saline solution at a pH of less than about 7.5,generate a cleansing amount of carbon dioxide and carbonic acid.Compositions of the latter type are preferred for their consumerconvenience, ease of manufacture, simple packaging requirements andcost.

Other ways to generate carbon dioxide and carbonic acid are possible.For example, an acidic composition can be packaged separately from anaqueous solution containing a carbonate compound. When a drop or two ofthe acidic composition is added to a contact lens storage casepre-filled with the aqueous solution containing a carbonate compound,carbon dioxide and carbonic acid would be generated.

A less convenient, but still effective method of adding carbon dioxideand carbonic acid into a contact lens storage case involves packaging anaqueous composition (e.g., purified water or a buffered, isotoniccomposition, such as Opti-Free or Opti-One Express) containing dissolvedcarbon dioxide in a polyethylene terephthalate (PET) bottle underpressure, much like soft drinks are packaged in PET bottles. Once thecap is removed from the bottle, the carbon dioxide composition can becombined in a suitable container with a contact lens for cleaning. Afterreplacing the bottle cap, the dissolved carbon dioxide will escape fromthe bottle. PET bottles containing dissolved carbon dioxide for this usewill, therefore, likely contain only enough product for one cleaning ora “single-use.”

Still another way to generate carbon dioxide and carbonic acid in a lenscase involves combining an aqueous buffered, isotonic, preservedsolution containing a carbonate component with heat and/or a metalcatalyst fixed in the lens case. For example, a metal catalyst coatingon the walls of the lens storage case would react with the carbonatefrom the aqueous buffered, isotonic, preserved solution to producecarbon dioxide and carbonic acid.

Because the compositions of the present invention do not require enzymesto effectively clean soiled contact lenses, they may be sterilized usingconventional gamma irradiation sterilization techniques. When combinedwith a disinfecting solution or a rinsing, disinfecting and storagesolution, the burden upon the disinfectant is lower in the case of thecleaning compositions of the present invention than in the case ofconventional enzyme-containing cleaning compositions.

In a preferred embodiment of the present invention, the composition ofthe present invention is prepared in the form of an effervescent tablet.As those skilled in art appreciate, the effervescent tablet must containa basic component and an acidic component, so that upon dissolutionappropriate reactions occur to generate carbon dioxide and carbonicacid. If the tablet does not directly contain both acidic and basiccomponents, it may be formulated with just one of these ingredients,with the other ingredient added by way of the diluent composition. Inthis way, in the event the tablet is exposed to moisture during storage,for example, premature acid-base reactions can be minimized or avoided.Suitable effervescent components include the carbonate family of basiccompounds and inorganic or organic acidic compounds. The effervescenttablet can be formulated as a layered tablet, with one layer comprisingthe acidic component and the other the basic component, in order tominimize premature acid-base reactions during storage.

Among the carbonate family of basic compounds, preferred effervescentcomponents for use in the compositions of the present invention aresodium carbonate, sodium bicarbonate, glycine carbonate, potassiumcarbonate, potassium bicarbonate, potassium dihydrogencitrate, andcalcium carbonate. Most preferred is sodium bicarbonate.

Preferred acidic components for use in the compositions of the presentinvention are citric acid, adipic acid, tartaric acid, maleic acid,boric acid, benzoic acid, hydroxybenzoic acid, methoxybenzoic acid,mandelic acid, malonic acid, lactic acid, pyruvic acid, glutaric acid,aspartic acid, hydrochloric acid, oxalic acid, salicylic acid, succinicacid, and acetic acid. The most preferred acidic effervescent componentsare citric acid and adipic acid, and combinations of these two acids.

As those skilled in the art appreciate, the amounts of the basic andacidic components required in the compositions of the present inventionto generate an amount of carbon dioxide and carbonic acid sufficient toclean a soiled contact lens will depend on a number of factors,including the particular basic and acidic components chosen, the periodof time available for cleaning, the type and extent of the deposits onthe soiled lens to be cleaned, etc. Generally, however, the amount ofcarbon dioxide required will be at least 5 mg or more.

In the case of sodium bicarbonate and citric acid, the amount of thebasic component will typically be from 10 to 200 mg, and the amount ofthe acidic component will typically be from 5 to 65 mg. Particularly ifacidic and basic component concentrations in the lower portion of theseranges are employed, additional ingredients, such as sodium chloride,mannitol, sorbitol, glucose, fructose or lactose, can be added to thebasic and acidic effervescent components as fillers, excipients, bulkingagents or tonicity agents.

Without being bound to any theory, it is believed that CO₂ produced fromthe reaction between the acidic and basic effervescent components of thetablet compositions of the present invention in the presence of watergenerates carbonic acid.

In some cases, it is desirable to include a lubricant in effervescenttablet compositions in order to facilitate the manufacture of tablets.Suitable lubricants and their typical concentrations (in weight percentbased on total tablet composition) include polyethylene glycol 3,350(0.05-10%); polyethylene glycol 8,000 (1-10%); sodium benzoate (1-10%);vegetable oils (1-4%); talc (1-5%); boric acid (0.5-5%); and sodiumborate (0.5-5%). The preferred lubricant for use in the tabletcompositions of the present invention is polyethylene glycol 3,350.

In addition to the basic and acidic effervescent tablet ingredientsdescribed above, the tablet composition of the present invention mayalso contain other excipients conventionally employed in ophthalmictablet compositions such as lactose anhydrous, lactose, mannitol,sorbitol, glucose, fructose; compressible sugar; or sodium chloride.Sodium chloride can be used to adjust the tonicity of the tablet inorder to cause the solution resulting from the dissolution of the tabletto be isotonic. Though it is not an essential ingredient, the preferredtablet compositions of the present invention may contain lactoseanhydrous as a filler. As mentioned above, however, the tabletcompositions do not contain polymeric beads, an enzyme, or cleansingamounts of surfactants. The compositions do not contain a disinfectingamount of hydrogen peroxide.

The tablet compositions of the present invention are obtained usingtableting procedures known in the art. Generally, the tabletingprocedures may be summarized as follows.

1. The formulation ingredients are weighed and sized using anoscillating granulator with an 18 to 40 mesh screen (may use any of 18,20, 26, 30, 33 or 40 mesh screen).

2. The materials are then blended using a twin shell P-K blender untiluniform (generally about 30 minutes or less). Alternatively, a coneblender may be used.

3. Tablets are compressed using suitable tooling on a suitable tabletpress.

4. Tablet weight can be adjusted from about 35 to 300 mg (a preferredtablet weight is about 73 mg).

5. The tablet hardness ranges from 2 to 8 strong cobb units.

6. Tablets are then pressed and strip packaged.

7. The strip packaged tablets can then be sterilized using γ (gamma)irradiation.

The effervescent tablet compositions of the present invention may be isdissolved in purified water or a simple saline solution in a contactlens holder (such as a 5 mL plastic vial). The soiled contact lens maybe placed in the lens holder containing purified water or salinesolution prior to, or just after, the effervescent tablet is added tothe holder. Once the tablet is dissolved, typically in about 60 secondsor less, the soiled contact lens is contacted with the resultingsolution for a time sufficient to achieve effective cleaning. The pH ofthe resulting solution is less than about 7.5. The time required foreffective cleaning will vary depending upon the type and extent ofdeposits on the lens, etc., but is generally less than about 4 hours andpreferably less than about 1 hour.

In one embodiment, the present invention provides a method of cleaningcontact lenses comprising dissolving a tablet consisting essentially ofa basic effervescent component and an acidic effervescent component inan aqueous composition at a pH of less than about 7.5 such that acleansing amount of carbon dioxide and carbonic acid are produced andcontacting the contact lens with the carbon dioxide and carbonic acid,wherein the tablet optionally contains one or more ingredients selectedfrom the group consisting of fillers, lubricating agents, bulking agentsand tonicity agents, but does not contain polymeric beads, an enzyme, acleansing amount of a surfactant, or a disinfecting amount of hydrogenperoxide.

Alternatively, a simple, one-step cleaning and disinfecting regimen isobtained when the effervescent tablet compositions of the presentinvention are dissolved in an aqueous composition selected from thegroup consisting of disinfecting solutions andrinsing/disinfecting/storage solutions, instead of a purified water or asimple saline solution as described above. Suitable disinfectantsinclude polyquaternium-1, the disinfectant contained in Opti-Free®Rinsing, Disinfecting & Storage Solution, but do not include hydrogenperoxide. Accordingly, the compositions of the present invention do notinclude a disinfecting amount (e.g., about 0.01 to less than 0.5% w/v)of hydrogen peroxide, nor are they combined with aqueous compositionscomprising a disinfecting amount of hydrogen peroxide.

The following examples are presented to illustrate various aspects ofthe present invention, but are not intended to limit the scope of theinvention in any respect.

Tableting Procedure: All tablets referred to in the examples presentedbelow were prepared according to the following procedure in 20% or lowerhumidity conditions:

a) The formulation ingredients were weighed, sized using an oscillatinggranulator with a suitable mesh screen (18-40 mesh), and blended using atwin shell Patterson-Kelly blender for 30 minutes.

b) Tablets were compressed using a {fraction (3/16)}″ diameter tablettooling on a Stokes B-2 tablet press.

c) The tablets weighed an average of 73 mg/tablet, with a hardness ofabout 5.0-7.0 Strong Cobb Units.

d) Tablet disintegration time was measured in purified water and foundto be about 35-45 seconds for each of the tablets mentioned in Examples1 and 2.

Cleaning Efficacy

Cleaning efficacy was determined using soiled contact lenses. Soiledlenses were obtained from two sources: (1) human study participants(“human-worn lenses”) and (2) a laboratory where lysozyme, mucin andlipids were intentionally deposited upon the lenses (“laboratorydeposited lenses”).

Cleanliness of the lenses was evaluated as follows. The loosely-bounddeposits on soiled lenses were removed by gently rubbing both surfacesof the lenses with Unisol Plus® saline solution in the palm of a hand.The lenses were then visually examined for remaining deposits and ratedaccording to the Rudko system for classification of lens deposits. SeeTable 1 below (Equipment: Bausch and Lomb tweezers; Bausch and Lombspotlight; Sorgs lint-free towel; and Vigor measuring magnifier7X#EL470).

TABLE 1 Rudko Lens Deposit Classification System Class Heaviness ofDeposit I Clean II Visible under oblique light when wet or dry using 7×magnification III Visible when dry with the unaided eye IV Visible whenwet with the unaided eye Type of Deposit C Crystalline G Granular FFilmy Extent of Deposit A  0-25% of lens B 25-50% of lens C 50-75% oflens D 75-100% of lens Definitions C: Crystalline deposits comprised ofcrystal groups which may be scattered or layered and are usuallyiridescent, depending upon the illumination. G: Granular depositsconsisting of fine granulation, usually in mass form. F: Film and hazesconsisting of castings which are not granular or crystalline. The hazesoften have a bluish tint.

After their initial cleanliness evaluation, the lenses were soaked inthe designated cleaning solution for the indicated period of time (30,60, 120 or 240 minutes) and again rated for deposits according to thecleanliness evaluation system described above. The lenses which were notcleaned after 1 hour were exposed to same cleaning solution foradditional time (2 and 4 hrs), and rated again.

EXAMPLE 1 Preparation of Citric Acid/Sodium Bicarbonate Tablets

Effervescent tablets were formulated according to the proceduresdescribed above using following ingredients:

Gm/10,000 Ingredients mg/Tablet Tablets *Citric Acid, USP, Anhydrous21.0 210.0 *Sodium Bicarbonate, USP, Powder 48.0 480.0 **PolyethyleneGlycol, 3350, USP,  4.0  40.0 Fine Powder Total 73.0*** 730.0*Effervescent components **Tablet Lubricant ***Theoretically, 73 mgeffervescent tablet gives 25 mg of carbon dioxide

EXAMPLE 2 Preparation of Adipic Acid/Sodium Bicarbonate Tablets

Effervescent tablets were formulated according to the proceduresdescribed above using following ingredients:

Gm/10,000 Ingredients mg/Tablet Tablets *Adipic Acid, N.O.C. 38.6 386*Sodium Bicarbonate, USP, Powder 34.4 344 Total 73.0** 730.0*Eftervescent components **Theoretically, 73 mg eftervescent tabletgives 25 mg of carbon dioxide

EXAMPLE 3 Preparation of Sodium Citrate Solution

A cleaning solution was formulated using following ingredients:

Ingredients amount Sodium Citrate 2 g Purified Water q.s. to 100 mL

EXAMPLE 4 Disintegration Time and Solution pH for Tablets of Example 1

The disintegration time and pH of solution were determined afterdissolving one and two tablets of Example 1, respectively, in separatevials each containing 5 mL of purified water. The results are shown inTable 2 below.

TABLE 2 1 Tablet in 5 mL Diluent 2 Tablets in 5 mL Diluent Observ-Observ- ation Disintegration ation Disintegration # Time (sec) pH # Time(sec) pH 1 35 6.65 1 35, 35 6.54 2 36 6.43 2 38, 40 6.50 3 37 6.63 3 42,42 6.53 4 40 6.37 4 40, 42 6.54 5 40 6.38 5 40, 40 6.55

EXAMPLE 5 Cleaning Efficacy of Tablets of Example 1 (1 Tablet/5 mLDiluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets ofExample 1 was evaluated by placing one 73 mg tablet into 5 mL of diluent(purified water). Theoretically, a 73 mg tablet gives 25 mg of carbondioxide. After the tablet was dissolved, soiled human worn soft contactlenses were rated and placed in the solution. After soaking in thesolution for one hour, the lenses were rated again. If the lens was notcleaned after one hour, the lens was returned to the solution for anadditional hour. If the lens was not cleaned after the second hour, thelens was returned to the solution for an additional two hours andevaluated again. Eight soft contact lenses were evaluated. The resultsare presented below in Table 3.

TABLE 3 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets (1Tablet/5 mL Diluent) With Soiled Human Worn Soft Contact LensesCleanliness Rating Before After Cleaning Lens # Lens Type Lens AgeCleaning 1 Hr 2 Hr 4 Hr 1 Group II 2 years III FA III FA I — 2 Group II2 years III FC III FA I — 3 Group II 6 months III FC III FA I — 4 GroupII 6 months III FB III FA III FA I 5 Group IV 8 months III FC III FC I —6 Group IV 8 months III FB III FB I — 7 Group IV 6 months III FA III FAI — 8 Group IV 6 months III FA III FA I —

EXAMPLE 6 Cleaning Efficacy of Tablets of Example 1 (2 Tablets/5 mLDiluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets ofExample 1 was evaluated as described in Example 5 above, except that inthis case two 73 mg tablets were placed into 5 mL of diluent (purifiedwater). Theoretically, two 73 mg tablets give 50 mg of carbon dioxide.Twelve soft contact lenses were evaluated. The results are shown inTable 4 below.

TABLE 4 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets (2Tablets/5 mL Diluent) With Soiled Human Worn Soft Contact LensesCleanliness Rating Lens Before After Cleaning Lens # Type Lens AgeCleaning 1 Hr 2 Hr 4 Hr 1 Group IV  6 months III FC III FA I — 2 GroupIV  6 months III FB I — 3 Group I  6 months III FC III FA I — 4 Group I 6 months III FB III FA I — 5 Group IV  2 months IV FD I — 6 Group IV  2months IV FD I — 7 Group I  6 months III FA I — 8 Group I  6 months IIIFC I — 9 Group I 12 months III FA III FA I — 10 Group I 12 months III FAI — 11 Group IV  6 months III FB I — 12 Group IV  6 months III FB I —

EXAMPLE 7 Cleaning Efficacy of Tablets of Example 1 (3 Tablets/5 mLDiluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets ofExample 1 was evaluated as described in Example 5 above, except that inthis case three 73 mg tablets were placed into 5 mL of diluent (purifiedwater). Theoretically, three 73 mg tablets give 75 mg of carbon dioxide.Four soft contact lenses were evaluated. The results are shown in Table5 below.

TABLE 5 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets (3Tablets/5 mL Diluent) With Soiled Human Worn Soft Contact LensesCleanliness Rating Lens Lens Before After Cleaning Lens # Type AgeCleaning 1 Hr 2 Hr 4 Hr 1 Group I 6 months III FA I — 2 Group I 6 monthsIII FC I — 3 Group I 6 months III FD I — 4 Group I 6 months III FB I —

EXAMPLE 8 Cleaning Efficacy of Tablets of Example 1 (1 Tablet/5 mLDiluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets ofExample 1 was evaluated as described in Example 5 above, except that inthis case six soiled human worn rigid gas permeable contact lenses wereevaluated. The results are shown in Table 6 below.

TABLE 6 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets (1Tablet/5 mL Diluent) With Soiled Human Worn Rigid Gas Permeable LensesCleanliness Rating Lens Before After Cleaning Lens # Type Lens AgeCleaning 1 Hr 2 Hr 4 Hr 1 RGP 12 months III FB III FA I — 2 RGP  6months III FC I — 3 RGP  6 months III FD I — 4 RGP  6 months III FA I —5 RGP  3 months III FA I — 6 RGP  3 months III FA I —

EXAMPLE 9 Cleaning Efficacy of Tablets of Example 1 (2 Tablets/5 mLDiluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets ofExample 1 was evaluated as described in Example 6 above, except that inthis case soiled human worn rigid gas permeable contact lenses wereevaluated. Four lenses were evaluated. The results are shown in Table 7below.

TABLE 7 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets (2Tablets/5 mL Diluent) With Soiled Human Worn Rigid Gas Permeable LensesCleanliness Rating Lens Before After Cleaning Lens # Type Lens AgeCleaning 1 Hr 2 Hr 4 Hr 1 RGP  6 months III FA I — 2 RGP 12 months IIIFA I — 3 RGP 12 months III FA I — 4 RGP 12 months III FA I —

EXAMPLE 10 Cleaning Efficacy of Tablets of Example 2 (2 Tablets/5 mLDiluent)

The cleaning efficacy of the adipic acid/sodium bicarbonate tablets ofExample 2 was evaluated by placing two 73 mg tablets into 5 mL ofdiluent (Unisol Plus Saline Solution). Theoretically, two 73 mg tabletsgive 50 mg of carbon dioxide. After the tablets dissolved, soiled humanworn soft contact lenses or laboratory deposited soft contact lenseswere placed in the solution and evaluated after soaking for one hour.Ten lenses were evaluated. After one hour of soaking, all ten lenseswere effectively cleaned. The results are presented below in Table 8.

TABLE 8 Cleaning Efficacy of Adipic Acid/Sodium Bicarbonate Tablets (2Tablets/5 mL Diluent) With Soiled Human Worn and Laboratory DepositedSoft Contact Lenses Cleanliness Rating Lens Before Cleaning AfterCleaning # Initial 30 Min 60 Min 120 Min Human Worn Soft Lenses 5 IIIFBIIIFA I — 6 IIIFA IIIFA I — 7 IIIFB IIIFA I — 8 IIIFB IIIFA I — 24 IVFCIIIFB I — 25 IVFC IIIFA I — 26 IVFD IIIFB I — Laboratory Deposited SoftLenses 1 IVFD IIIFA I — 2 IVFD IIIFB I — 3 IVFC IIIFA I —

EXAMPLE 11 Cleaning Efficacy of Tablets of Example 2 (with CO₂ removedfrom solution)

The experiment of Example 10 above was repeated, except that the CO₂ wasremoved from the solution prior to exposing the soiled lenses to thesolution. Cleaning solutions were prepared by dissolving two tablets ofExample 2 in 5 mL of Unisol Plus Saline Solution. The cleaning solutionswere then heated in a microwave oven at low setting for 2 minutes toremove CO₂. The soiled lenses (human worn and lab deposited) were thensoaked in the cleaning solution for the designated time and rated. Theresults, shown below in Table 9, for the eight lenses evaluated show nocleaning after 120 minutes.

TABLE 9 Cleaning Efficacy of Adipic Acid/Sodium Bicarbonate Tablets(After CO₂ Removed) With Soiled Human Worn and Laboratory Deposited SoftContact Lenses Cleanliness Rating Lens # of Before Cleaning AfterCleaning # Tablets Initial 30 Min 60 Min 120 Min Human Worn Soft Lenses9 2 IVFD IVFD IVFD IVFD 10 2 IIIFB IIIFB IIIFB IIIFB 11 2 IIIFA IIIFAIIIFA IIIFA 12 2 IIIFA IIIFA IIIFA IIIFA 30 2 IVFC IVFC IVFC IVFC 31 2IVFD IVFD IVFD IVFD Laboratory Deposited Soft Lenses 9 2 IVFD IVFD IVFDIVFD 10 2 IVFD IVFD IVFD IVFD

EXAMPLE 12 Cleaning Efficacy of Tablets of Example 1 in Saline Solution(2 Tablets/5 mL Diluent)

The cleaning efficacy of the citric acid/sodium bicarbonate tablets ofExample 1 was evaluated as described in Example 6 above, except that inthis case the cleaning solutions were prepared by dissolving two tabletsof Example 1 in 5 mL of diluent (Unisol Plus Saline Solution). A totalof ten soiled (human worn and laboratory deposited) soft contact lenseswere evaluated. The results are shown in Table 10 below. All ten lenseswere cleaned within 60 minutes.

TABLE 10 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets (2Tablets/5 mL Diluent) With Soiled Human Worn Contact Lenses CleanlinessRating Lens # of Before Cleaning After Cleaning # Tablets Initial 30 Min60 Min 120 Min Human Worn Soft Lenses 1 2 IIIFA IIIFA I — 2 2 IIIFAIIIFA I — 3 2 IIIFB IIIFA I — 4 2 IIIFB IIIFA I — 27 2 IVFC IIIFA I — 282 IVFD IIIFB I — 29 2 IVFD IIIFA I — Laboratory Deposited Soft Lenses 42 IVFD IIIFA I — 5 2 IVFD IIIFA I — 6 2 IVFC IIIFA I —

EXAMPLE 13 Cleaning Efficacy of Tablets of Example 1 (with CO₂ removedfrom solution)

The experiment of Example 12 above was repeated, except that the CO₂ wasremoved from the cleaning solution prior to exposing the soiled lensesto the solution. Cleaning solutions were prepared by dissolving twotablets of Example 1 in 5 mL of Unisol Plus Saline Solution. Thecleaning solutions were then heated in a microwave oven at low settingfor 2 minutes to remove CO₂. The soiled lenses (human worn and labdeposited) were then soaked in the cleaning solution for the designatedtime and rated. The results, shown below in Table 11, for the eightlenses evaluated show essentially no cleaning after 120 minutes.

TABLE 11 Cleaning Efficacy of Citric Acid/Sodium Bicarbonate Tablets(After CO₂ Removed) With Soiled Human Worn and Laboratory Deposited SoftContact Lenses Cleanliness Rating Lens # of Before Cleaning AfterCleaning # Tablets Initial 30 Min 60 Min 120 Min Human Worn Soft Lenses13 2 IIIFB IIIFB IIIFB IIIFB 14 2 IIIFB IIIFB IIIFB IIIFA 15 2 IIIFBIIIFB IIIFB IIIFB 16 2 IIIFB IIIFB IIIFB IIIFB 32 2 IVFD IVFB IVFD IVFD33 2 IVFC IVFB IVFB IVFB Laboratory Deposited Soft Lenses 7 2 IVFC IVFCIVFC IVFC 8 2 IVFD IVFD IVFD IVFD

EXAMPLE 14 Cleaning Efficacy of Sodium Citrate Solution of Example 3

The cleaning efficacy of the cleaning solution of Example 3 wasevaluated as follows. Eleven soiled lenses (human worn) were rated fordeposits, then soaked in the cleaning solution for the designated timeand rated again. The results, shown below in Table 12 show no effectivecleaning after 120 minutes.

TABLE 12 Cleaning Efficacy of Sodium Citrate Solution With Soiled HumanWorn Soft Contact Lenses Cleanliness Rating Lens Before Cleaning AfterCleaning # Initial 30 Min 60 Min 120 Min Human Worn Soft Lenses 17 IIIFBIIIFB IIIFB IIIFB 18 IIIFB IIIFB IIIFB IIIFB 19 IVFD IVFD IVFC IVFC 20IIIFB IIIFB IIIFB IIIFB 21 IIIFB IIIFB IIIFB IIIFB 22 IIIFB IIIFB IIIFBIIIFB 23 IIIFA IIIFA IIIFA IIIFA 1A IIIFC IIIFC IIIFC IIIFC 2A IIIFBIIIFB IIIFB IIIFB 3A IVFD IIIFD IIIFD IIIFD 4A IVFC IVFC IVFC IVFC

EXAMPLE 15 Recleaning of Laboratory Deposited Soft Lenses with Tablet ofExample 1

Soiled (laboratory deposited) lenses #7 and #8 (Table 11) in Example 13above which were not cleaned when exposed to a cleaning solutionprepared by dissolving two tablets of Example 1 in 5 mL of Unisol PlusSaline Solution and then eliminating the CO₂ by heating in a microwaveoven on a low setting for two minutes, were recleaned by subjecting themto a cleaning solution prepared by dissolving one tablet of Example 1 in5 mL of Unisol Plus Saline Solution. As shown in Table 13 below, bothlenses were effectively cleaned after 120 minutes. This experimentdemonstrates that the presence of CO₂ is necessary for effectivecleaning of soiled lenses.

TABLE 13 Recleaning of Soiled (Laboratory Deposited) Soft Contact LensesUsing Tablet of Example 1 (1 Tablet/5 mL Diluent). Cleanliness RatingBefore Lens Cleaning After Cleaning # Initial 30 Min 60 Min 120 Min 7IVFC IIIFC IIIFC I 8 IVFD IIIFB IIIFB I

EXAMPLE 16 Recleaning of Laboratory Deposited Soft Lenses with Tablet ofExample 2

Soiled (laboratory deposited) lenses #9 and #10 (Table 9) in Example 11above which were not cleaned when exposed to a cleaning solutionprepared by dissolving two tablets of Example 2 in 5 mL of Unisol PlusSaline Solution and then eliminating the CO₂ by heating in a microwaveoven on a low setting for two minutes, were recleaned by subjecting themto a cleaning solution prepared by dissolving one tablet of Example 2 in5 mL of Unisol Plus Saline Solution. As shown in Table 14 below, bothlenses were effectively cleaned after 120 minutes. This experimentdemonstrates that the presence of CO₂ is necessary for effectivecleaning of soiled lenses.

TABLE 14 Recleaning of Soiled (Laboratory Deposited) Soft Contact LensesUsing Tablet_of Example 2 (1 Tablet/5 mL Diluent). Cleanliness RatingBefore Lens Cleaning After Cleaning # Initial 30 Min 60 Min 120 Min 9IVFD IIIFD IIIFA I 10 IVFD IIIFB IIIFB I

EXAMPLE 17 Recleaning of Human Worn Soft Lenses with Tablet of Example 1

Soiled (human worn) lenses #17-22 (Table 12) in Example 14 above whichwere not cleaned when exposed to the sodium citrate cleaning solution ofExample 3, were recleaned by subjecting to them to a cleaning solutionprepared by dissolving two tablets of Example 1 in 5 mL of Unisol PlusSaline Solution. As shown in Table 15 below, most lenses wereeffectively cleaned after 60 minutes and all lenses were effectivelycleaned after 120 minutes. This experiment demonstrates that thepresence of CO₂ is necessary for effective cleaning of soiled lenses.

TABLE 15 Recleaning of Soiled (Human Worn) Soft Contact Lenses UsingTablet of Example 1 (2 Tablet/5 mL Diluent). Cleanliness Rating BeforeLens Cleaning After Cleaning # Initial 30 Min 60 Min 120 Min 17 IIIFDIIIFA I — 18 IIIFB IIIFA I — 19 IVFD IIIFC IIIFA I 20 IIIFB IIIFA I — 21IIIFB IIIFA I — 22 IIIFB IIIFA I —

EXAMPLE 18 Recleaning of Human Worn Soft Lenses with Tablet of Example 2

Soiled (human worn) lenses #23 and 1A-4A (Table 12) in Example 14 abovewhich were not cleaned when exposed to the sodium citrate cleaningsolution of Example 3, were recleaned by subjecting them to a cleaningsolution prepared by dissolving two tablets of Example 2 in 5 mL ofUnisol Plus Saline Solution. As shown in Table 15 below, most lenseswere effectively cleaned after 60 minutes and all lenses wereeffectively cleaned after 120 minutes. This experiment demonstrates thatthe presence of CO₂ is necessary for effective cleaning of soiledlenses.

TABLE 16 Recleaning of Soiled (Human Worn) Soft Contact Lenses UsingTablet of Example 2 (2 Tablet/5 mL Diluent). Cleanliness Rating BeforeLens Cleaning After Cleaning # Initial 30 Min 60 Min 120 Min 23 IIIFA I— — 1A IIIFC IIIFC IIIFC I 2A IIIFB IIIFA I — 3A IIIFD IIIFA I — 4A IVFCIIIFB I —

EXAMPLE 19 Normalization of Cleaning Data for Human Worn Soft ContactLenses #17-22

For comparison purposes, the cleaning results for soiled (human worn)soft contact lenses #17-22 in Table 12 were normalized with the data inTable 15. In order to plot the cleaning efficacy data against time, thelens deposit rating obtained using the Rudko rating system (Tables 12and 15) was converted to a numerical rating using the conversion keyshown below in Table 17. The number assigned for each Rudko rating foreach lens was added for each time interval and the data normalized bydividing with highest number. The normalized data for cleaning efficacywith 2% Sodium Citrate Solution of Example 3 and cleaning efficacy withthe citric acid/sodium bicarbonate tablets of Example 1 appears in Table18 below and is summarized in FIG. 1. This normalized data illustratesthat complete, effective cleaning was achieved with the CO₂-containingsolution in two hours. However, most of the lenses were cleaned in onehour. In the absence of carbon dioxide, no cleaning was achieved. Thisis also evident from the data shown in Table 11.

TABLE 17 Rudko Lens Deposit Classification System Conversion of RudkoDeposit Classification to Numerals Rudko Classification Numeral AssignedI - Clean Lens 0.00 IIFA 1.25 IIFB 1.50 IIFC 1.75 IIFD 2.00 IIIFA 2.25IIIFB 2.50 IIIFC 2.75 IIIFD 3.00 IVFA 3.25 IVFB 3.50 IVFC 3.75 IVFD 4.00

TABLE 18 Numerical Equivalent of Rudko Rating for Cleaning Efficacy Data(Human Worn Lenses #17-22) Lens Before Cleaning After Cleaning # Initial30 Min 60 Min 120 Min Data from Table 12 (Without CO₂) 17 2.50 2.50 2.502.50 18 2.50 2.50 2.50 2.50 19 4.00 4.00 3.75 3.75 20 2.50 2.50 2.502.50 21 2.50 2.50 2.50 2.50 22 2.50 2.50 2.50 2.50 Total 16.50 16.5016.25 16.25 Normalized 1.00 1.00 0.985 0.985 Data from Table 15 (WithCO₂) 17 2.50 2.25 0.0 — 18 2.50 2.25 0.0 — 19 4.00 2.75 2.25 0.0 20 2.502.25 0.0 0.0 21 2.50 2.25 0.0 0.0 22 2.50 2.25 0.0 0.0 Total 16.50 14.002.25 0.0 Normalized 1.00 0.848 0.136 0

EXAMPLE 20 Osmolality and pH Measurements

Fresh samples of various cleaning solutions were prepared and theirosmolality and pH determined. Osmolality and pH of Unisol Plus were alsodetermined as a control. The data is shown below in Table 19.

TABLE 19 Osmolality and pH Measurements Osmolality # Sample mOsm/KgpH 1. Unisol Plus Saline Solution 300 7.38 2. 2% Sodium Citrate inPurified Water (Ex. 3) 186 7.85 3. Two Adipic Acid Based Tablets (Ex. 2)568 5.32 dissolved in 5 mL of Unisol Plus 4. Two Citric Acid BasedTablets (Ex. 1) 616 7.02 dissolved in 5 mL of Unisol Plus 5. One AdipicAcid Based Tablet (Ex. 2) 441 5.33 dissolved in 5 mL of Unisol Plus 6.One Citric Acid Based Tablet (Ex. 1) 461 7.09 dissolved in 5 mL ofUnisol Plus 7. Two Adipic Acid Based Tablets (Ex. 2) 637 5.16 dissolvedin 5 mL of Unisol Plus and heated to remove CO₂ 8. Two Citric Acid BasedTablets (Ex. 1) 646 8.11 dissolved in 5 mL of Unisol Plus and heated toremove CO₂

The invention has been described by reference to certain preferredembodiments; however, it should be understood that it may be embodied inother specific forms or variations thereof without departing from itsspirit or essential characteristics. The embodiments described above aretherefore considered to be illustrative in all respects and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than by the foregoing description.

What is claimed is:
 1. A method of cleaning a soiled contact lenscomprising the steps of dissolving an effervescent tablet compositioncapable of generating a cleansing amount of carbon dioxide and carbonicacid in an aqueous composition having a pH of less than about 7.5 toform a cleaning solution, and contacting the soiled lens with thecleaning solution for a time sufficient to clean the soiled lens,wherein the effervescent tablet composition excludes polymeric beads, anenzyme, a cleansing amount of a surfactant, and a disinfecting amount ofhydrogen peroxide, and further provided that the effervescent tablet isa layered tablet comprising a first layer containing a compound selectedfrom the group consisting of alkali carbonate compounds but lacking anacidic compound and a second layer containing a compound selected fromthe group consisting of organic and inorganic acidic compounds butlacking an alkali carbonate compound.
 2. The method of claim 1 whereinthe first layer comprises an alkali carbonate compound selected from thegroup consisting of sodium carbonate, sodium bicarbonate, glycinecarbonate, potassium carbonate, potassium bicarbonate, potassiumdihydrogencitrate, and calcium carbonate; and the second layer comprisesa compound selected from the group consisting of citric acid, adipicacid, tartaric acid, maleic acid, boric acid, benzoic acid,hydroxybenzoic acid, methoxybenzoic acid, mandelic acid, malonic acid,lactic acid, pyruvic acid, glutaric acid, aspartic acid, hydrochloricacid, oxalic acid, salicylic acid, succinic acid, and acetic acid. 3.The method of claim 2 wherein the first layer comprises sodiumbicarbonate and the second layer comprises an acidic compound selectedfrom the group consisting of citric acid, adipic acid and combinationsof citric and adipic acids.
 4. The method of claim 1 wherein the aqueouscomposition is selected from the group consisting of purified water;saline solutions; disinfecting solutions; andrinsing/disinfecting/storage solutions; provided that the aqueouscomposition does not contain a disinfecting amount of hydrogen peroxide.5. A method of cleaning a soiled contact lens comprising the steps ofdissolving an effervescent tablet composition in an aqueous compositionhaving a pH of less than about 7.5 to form a cleaning solution, andcontacting the soiled lens with the cleaning solution for a timesufficient to clean the soiled lens, wherein the effervescent tabletcomposition excludes polymeric beads, an enzyme, a cleansing amount of asurfactant, and a disinfecting amount of hydrogen peroxide, and furtherprovided that only one of the effervescent tablet and the aqueouscomposition contains an alkali carbonate compound but no acidiccomponent, and the other of the effervescent table and the aqueouscomposition contains an acidic component but no alkali carbonatecompound, such that when the effervescent tablet is dissolved in theaqueous composition a cleansing amount of carbon dioxide and carbonicacid is generated.
 6. A method of cleaning a soiled contact lenscomprising contacting the soiled lens with an aqueous composition havinga pH of less than about 7.5 comprising a cleansing amount of carbondioxide and carbonic acid for a time sufficient to clean the soiledlens, wherein the composition excludes polymeric beads, an enzyme, acleansing amount of a surfactant, and a disinfecting amount of hydrogenperoxide, and wherein the composition is formed by combining separatelypackaged first and second aqueous compositions, where the first aqueouscomposition comprises an alkali carbonate compound but lacks an acidiccomponent selected from the group consisting of inorganic and organicacids, and the second aqueous composition comprises an acidic componentselected from the group consisting of inorganic and organic acids butlacks an alkali carbonate compound.